A high-density plasma chemical vapor deposition (HDP-CVD) technique is generally adopted for depositing an insulating film in a groove portion formed on a semiconductor substrate with 1.0 or more of a high aspect ratio (a ratio of a groove depth to an opening width), for example. In recent years, a hydrogen-molecule (H2) added HDP-CVD technique has been employed. Adding H2 in deposition makes it possible to perform the deposition while suppressing opening blockage due to overhang in an upper portion of the groove. As a result, since the deposition can prevent formation of voids in an insulating film buried in the groove, the insulating film burying property in the groove can be improved.
Since miniaturization results in further heightening the aspect ratio to 3.0 or higher, for example, it is essential to add H2 in the application of the HDP-CVD technique. However, a deoxidization by H2 causes a deficiency of oxygen atoms in the insulating film to affect quality of the insulating film. Thus, it is difficult to simultaneously satisfy the requirements for both insulating film burying property and quality of the insulating film. Such conventional technique is disclosed in U.S. Pat. Nos. 6,596,653 and 6596,654.